Recently, owing to population growth, it is often warned that food production in the world is likely to become an urgent subject needing to be solved in the near future, and importance is attached to albuminous fisheries products. Since fishing resources have a tendency to decrease, hope is pinned on the production of animal protein by aquaculture. Many kinds of living things have become extinct or are on the brink of extinction, and biodiversity is being lost. Aquatic animals are resources having a bright future. Various genetic resources are desired to be protected and utilized.
Also desired are various stocking methods which, with the increase of export and import of seafood, make it possible to use fishes as refrigerated fishes, live fishes or fresh fishes, as well as arts of exhibiting or breeding aquatic animals at aquariums and other facilities.
Crustacea are important aquatic animals as products or food for supporting production. There are a great many kinds of crustacea. Crustacea are hopeful genetic resources. Arthropods are the largest group of animals and occupy more than ¾ of all the kinds of animals on earth. It is said that there are about 30,000 kinds of crustacea which are arthropods living in water. Typical crustacea include crabs (Brachyura), hermit crabs (Anomura), and shrimps and lobsters (Natantia, Reptantia) which are called Decapoda. In coastal areas, there is a fear of crustacea resources being decreased. Stocking artificially cultured juveniles is thought to be a promising method for the recovery of the resources. These Decapoda are very popular foodstuffs. Recently, an increasing number of Decapoda are used as fresh or live foodstuffs, not refrigerated. Macrocheira kaempferi, which is the largest crab in the world, is popular at aquariums and other facilities. Therefore, the arts of rearing, cultivating or stocking crustacea are very important.
Marine crustacea have been reared, cultivated or stocked in surface sea water.
Japanese Patent Laid-Open Publication No. 2004-135562 discloses an art of cultivating ear shells, sea urchins or turban shells by means of a deep sea water. There are no patent publications which disclose an art of rearing, cultivating or stocking crustacea.
An art of rearing, cultivating or stocking marine crustacea by means of a surface sea water has the following disadvantages.
If marine crustacea such as Japanese lobsters (Metanephrops japonicus), sergestid shrimps (Sergia lucens), giant spider crabs (Macrocheira kaempferi) and deep sea red crabs (Chaceon granulatus) are reared, cultivated or stocked in the surface sea water, then there are disadvantages that it is difficult to rear, cultivate or stock the crustacea, the survival rate thereof is very low and the survival period thereof is short.
There are a large number of microorganisms such as viruses and bacteria within the surface sea water. If crustacea such as penaeid shrimps are reared, cultivated or stocked in the surface sea water, then there is a serious disadvantage that a large quantity of crustacea die owing to the infection of the microorganisms.
To avoid the infection, medicines or other foreign matters are added to the surface sea water. Said medicines or other foreign matters may affect the safety of the crustacea as foodstuffs.
If crustacea living in a cool water are to be reared, cultivated or stocked within the surface sea water, it is necessary to cool the water by means of a cooling device. The cooling device does not have a capacity large enough to keep supplying cooled fresh water to a container of the crustacea. The container usually has a water supply system of a circulating type or of a semi-circulating type. If such a water supply system is used, the surface sea water within the container may be contaminated by the accumulation of harmful matters and the increase of bacteria. These are disadvantages inevitable to rearing, cultivating or stocking crustacea by means of the surface sea water.